1. Field of the Invention
The invention relates to a method and a device for estimating motion in a sequence of moving images.
It is applied notably to making digital television systems and to reducing the rate of flow of data circulating in these systems.
2. Background Discussion
To estimate the motion or the displacement of points animating a sequence of images, known procedures consist in either matching the characteristic features of the images or using a differential estimation method that uses the spatial and temporal gradients of the representative points. However, in the latter case, it is difficult to master the initialization of the gradient algorithms used. For example, according to a first method, a known procedure lies in tracking the course of a number of characteristic points (angular points, curves etc.) over time to estimate their motion and initialize a gradient algorithm but, in this case, it is essential, before carrying out this tracking procedure, to resolve the problems of extracting and matching the angular points. This is a laborious process giving results that are as yet far from perfect.
Another known procedure, according to a second method, consists in bringing the mean square deviation of the local variations in inter-image luminance and, possibly, inter-frame luminance to the minimum and in then initializing the gradient algorithm by estimating the motion at the point preceding the current point on the same line. In this case, the convergence of the algorithm depends largely on the initialization stage used, and this stage is generally conducted in taking into account only those parameters defined in the immediate space-causal vicinity of the current point. Thus the field motions for each pair of images are computed independently, without having regard to the fact that these fields are necessarily inter-related from one image to the next.